Semiconductor device

ABSTRACT

A device includes a conductive feature, a dielectric layer, a bottom electrode via, and a liner layer. The dielectric layer is over the conductive feature. The bottom electrode via is in the dielectric layer and over the conductive feature. A topmost surface of the bottom electrode via is substantially flat. A liner layer cups an underside of the bottom electrode via. The liner layer has a topmost end substantially level with the topmost surface of the bottom electrode via.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/866,101, filed May 4, 2020, now U.S. Pat. No. 10,971,682, issued Apr.6, 2021, which is a continuation of U.S. patent application Ser. No.15/828,101, filed Nov. 30, 2017, now U.S. Pat. No. 10,644,231, issuedMay 5, 2020, all of which are herein incorporated by reference in theirentireties.

BACKGROUND

Semiconductor memories are used in integrated circuits for electronicapplications, including radios, televisions, cell phones, and personalcomputing devices, as examples. One type of semiconductor memory deviceinvolves spin electronics, which combines semiconductor technology andmagnetic materials and devices. The spins of electrons, through theirmagnetic moments, rather than the charge of the electrons, are used toindicate a bit.

One such spin electronic device is magnetoresistive random access memory(MRAM) array, which includes conductive lines (word lines and bit lines)positioned in different directions, e.g., perpendicular to each other indifferent metal layers. The conductive lines sandwich a magnetic tunneljunction (MTJ), which functions as a magnetic memory cell.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1-18 are cross-sectional views of the MRAM device at variousintermediate stages of manufacture according to various embodiments ofthe present disclosure.

FIG. 19 illustrates an integrated circuit including MRAM devices andlogic devices.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

According to some embodiments of this disclosure, a magnetoresistiverandom access memory (MRAM) device is formed. The MRAM device includes amagnetic tunnel junction (MTJ) stack. The MTJ stack includes a tunnelbarrier layer formed between a ferromagnetic pinned layer and aferromagnetic free layer. The tunnel barrier layer is thin enough (sucha few nanometers) to permit electrons to tunnel from one ferromagneticlayer to the other. A resistance of the MTJ stack is adjusted bychanging a direction of a magnetic moment of the ferromagnetic freelayer with respect to that of the ferromagnetic pinned layer. When themagnetic moment of the ferromagnetic free layer is parallel to that ofthe ferromagnetic pinned layer, the resistance of the MTJ stack is in alower resistive state, corresponding to a digital signal “0”. When themagnetic moment of the ferromagnetic free layer is anti-parallel to thatof the ferromagnetic pinned layer, the resistance of the MTJ stack is ina higher resistive state, corresponding to a digital signal “1”. The MTJstack is coupled between top and bottom electrode and an electriccurrent flowing through the MTJ stack (tunneling through the tunnelbarrier layer) from one electrode to the other is detected to determinethe resistance and the digital signal state of the MTJ stack.

According to some embodiments of this disclosure, the MRAM device isformed within a chip region of a substrate. A plurality of semiconductorchip regions is marked on the substrate by scribe lines between the chipregions. The substrate will go through a variety of cleaning, layering,patterning, etching and doping steps to form the MRAM devices. The term“substrate” herein generally refers to a bulk substrate on which variouslayers and device elements are formed. In some embodiments, the bulksubstrate includes silicon or a compound semiconductor, such as GaAs,InP, SiGe, or SiC. Examples of the layers include dielectric layers,doped layers, polysilicon layers or conductive layers. Examples of thedevice elements include transistors, resistors, and/or capacitors, whichmay be interconnected through an interconnect layer to additionalintegrated circuits.

FIG. 1 illustrates a wafer having a substrate 110 thereon. The substrate110 has a logic region LR where logic circuits are to be formed and acell region CR where memory devices are to be formed. The substrate 110includes an interlayer dielectric (ILD) layer or inter-metal dielectric(IMD) layer 112 with a metallization pattern 114 over the logic regionLR and the cell region CR. The ILD layer 112 may be silicon oxide,fluorinated silica glass (FSG), carbon doped silicon oxide,tetra-ethyl-ortho-silicate (TEOS) oxide, phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), Black Diamond® (Applied Materials ofSanta Clara, Calif.), amorphous fluorinated carbon, low-k dielectricmaterial, the like or combinations thereof. The metallization pattern114 may be aluminum, aluminum alloy, copper, copper alloy, titanium,titanium nitride, tantalum, tantalum nitride, tungsten, cobalt, thelike, and/or combinations thereof. Formation of the metallizationpattern 114 and the ILD layer 112 may be a dual-damascene process and/ora single-damascene process. The substrate 110 may also include activeand passive devices, for example, underlying the ILD layer 112. Thesefurther components are omitted from the figures for clarity. In someembodiments, a dielectric layer having a bottom electrode via (BEVA)therein is formed over the substrate, and a bottom electrode (BE) layeris formed over the dielectric layer.

Reference is then made to FIG. 2. An etch stop layer 120 and adielectric layer 140 are formed over the logic region LR and the cellregion CR of the substrate 110 in a sequence. The etch stop layer 120may have a high etch resistance to one or more subsequent etchingprocesses. The etch stop layer 120 may be formed of dielectric materialdifferent from the underlying ILD layer 112. For example, the ILD layer112 may be a silicon oxide layer, and the etch stop layer 120 may be asilicon nitride layer or a silicon carbide layer.

The dielectric layer 140 in some embodiments is silicon carbide (SiC),silicon oxynitride (SiON), silicon nitride (SiN), silicon dioxide, thelike, and/or combinations thereof. The dielectric layer 140 may be asingle-layered structure or a multi-layered structure. The dielectriclayer 140 may be formed by acceptable deposition techniques, such aschemical vapor deposition (CVD), atomic layer deposition (ALD), physicalvapor deposition (PVD), the like, and/or a combination thereof. In someembodiments, an anti-reflection layer ARL1, for example, a nitrogen-freeanti-reflection layer (NFARL) is optionally formed over the dielectriclayer 140. In some embodiments, a protective layer, such as analuminum-based layer may be formed between the etch stop layer 120 andthe dielectric layer 140.

Reference is then made to FIG. 3. Openings O1 are formed in theanti-reflection layer ARL1, the etch stop layer 120, and the dielectriclayer 140 in the cell region CR, and exposes portions of themetallization pattern 114. An exemplary formation method of the openingsO1 includes forming a patterned mask may over the anti-reflection layerARL1, and then etching the anti-reflection layer ARL1, the etch stoplayer 120, and the dielectric layer 140 through the patterned mask byone or more etching processes.

Reference is then made to FIG. 4. Bottom electrode vias (BEVA) 150 arethen formed within the openings O1. In some embodiments, at least one ofthe BEVAs 150 is a multi-layered structure and includes, for example, adiffusion barrier layer 152 and a filling metal 154 filling a recess inthe diffusion barrier layer 152. An exemplary formation method of theBEVAs 150 includes forming in sequence the diffusion barrier layer 152and the filling metal 154 into the openings O1, and performing aplanarization process, such as a chemical-mechanical polish (CMP)process, to remove excess materials of the filling metal 154 and of thediffusion barrier layer 152 outside the openings O1. The remainingdiffusion barrier layer 152 and the remaining filling metal 154 in theopenings O1 can serve as the BEVAs 150. In some embodiments, the BEVAs150 are electrically connected to an underlying electrical component,such as a transistor, through the metallization pattern 114.

In some embodiments, the diffusion barrier layer 152 is a titaniumnitride (TiN) layer or a tantalum nitride (TaN) layer, which can act asa suitable barrier to prevent metal diffusion. Formation of thediffusion barrier layer 152 may be exemplarily performed using CVD, PVD,ALD, the like, and/or a combination thereof. In some embodiments, thefilling metal 154 is titanium (Ti), tantalum (Ta), platinum (Pt),ruthenium (Ru), tungsten (W), aluminum (Al), copper (Cu), TiN, TaN, thelike, and/or combinations thereof. Formation of the filling metal 154may be exemplarily performed using CVD, PVD, ALD, the like, and/or acombination thereof.

Reference is made to FIG. 5. A blanket bottom electrode layer 160 isthen formed over the BEVAs 150 and over the dielectric layer 140, sothat the bottom electrode layer 160 extends along top surfaces of theBEVAs 150 and of the dielectric layer 140. The bottom electrode layer160 can be a single-layered structure or a multi-layered structure. Thebottom electrode layer 160 includes a material the same as the fillingmetal 154 in some embodiments. In some other embodiments, the bottomelectrode layer 160 includes a material different from the filling metal154. In some embodiments, the bottom electrode layer 160 is titanium(Ti), tantalum (Ta), platinum (Pt), ruthenium (Ru), tungsten (W),aluminum (Al), copper (Cu), TiN, TaN, the like, and/or a combinationthereof. Formation of the bottom electrode layer 160 may be exemplarilyperformed using CVD, PVD, ALD, the like, and/or a combination thereof.

In some embodiments, a buffer layer 170 is formed over the bottomelectrode layer 160. The buffer layer 170 may include a non-magneticmaterial. For example, the buffer layer 170 may include tantalum,aluminum, titanium, TiN, TaN, or the combination thereof. The bufferlayer 170 may be deposited by PVD, ALD, CVD, or MOCVD (metal-organicchemical vapor deposition). Alternatively, the buffer layer 170 isdeposited by an electroless plating process or other suitable process.

A resistance switching layer 180 is formed over the bottom electrodelayer 160 and the buffer layer 170. In some embodiments, the resistanceswitching layer 180 may be a magnetic tunnel junction (MTJ) structure.To be specific, the resistance switching layer 180 includes at least afirst magnetic layer, a tunnel barrier layer and a second magnetic layerare formed in sequence over the bottom electrode layer 160 and thebuffer layer 170.

In some embodiments, the first magnetic layer includes ananti-ferromagnetic material (AFM) layer over the buffer layer 170 and aferromagnetic pinned layer over the AFM layer. In the anti-ferromagneticmaterial (AFM) layer, magnetic moments of atoms (or molecules) align ina regular pattern with magnetic moments of neighboring atoms (ormolecules) in opposite directions. A net magnetic moment of the AFMlayer is zero. In certain embodiments, the AFM layer includes platinummanganese (PtMn). In some embodiments, the AFM layer includes iridiummanganese (IrMn), rhodium manganese (RhMn), iron manganese (FeMn), orOsMn. An exemplary formation method of the AFM layer includessputtering, PVD, ALD, e-beam or thermal evaporation, or the like.

The ferromagnetic pinned layer in the first magnetic layer forms apermanent magnet and exhibits strong interactions with magnets. Adirection of a magnetic moment of the ferromagnetic pinned layer can bepinned by an anti-ferromagnetic material (AFM) layer and is not changedduring operation of a resulting resistance switching element (e.g. a MTJstack) fabricated from the resistance switching layer 180. In certainembodiments, the ferromagnetic pinned layer includes cobalt-iron-boron(CoFeB). In some embodiments, the ferromagnetic pinned layer includesCoFeTa, NiFe, Co, CoFe, CoPt, or the alloy of Ni, Co and Fe. Anexemplary formation method of the ferromagnetic pinned layer includessputtering, PVD, ALD, e-beam or thermal evaporation, or the like. Insome embodiments, the ferromagnetic pinned layer includes a multilayerstructure.

The tunnel barrier layer is formed over the first magnetic layer. Thetunnel barrier layer can also be referred to as a tunneling layer, whichis thin enough that electrons are able to tunnel through the tunnelbarrier layer when a biasing voltage is applied to a resultingresistance switching element (e.g. a MTJ stack) fabricated from theresistance switching layer 180. In certain embodiments, the tunnelbarrier layer includes magnesium oxide (MgO), aluminum oxide (Al₂O₃),aluminum nitride (AlN), aluminum oxynitride (AlON), hafnium oxide (HfO₂)or zirconium oxide (ZrO₂). An exemplary formation method of the tunnelbarrier layer 172 includes sputtering, PVD, ALD, e-beam or thermalevaporation, or the like.

The second magnetic layer is formed over the tunnel barrier layer. Thesecond magnetic layer is a ferromagnetic free layer in some embodiments.A direction of a magnetic moment of the second magnetic layer is notpinned because there is no anti-ferromagnetic material in the secondmagnetic layer. Therefore, the magnetic orientation of this layer isadjustable, thus the layer is referred to as a free layer. In someembodiments, the direction of the magnetic moment of the second magneticlayer is free to rotate parallel or anti-parallel to the pinneddirection of the magnetic moment of the ferromagnetic pinned layer inthe first magnetic layer. The second magnetic layer may include aferromagnetic material similar to the material in the ferromagneticpinned layer in the first magnetic layer. Since the second magneticlayer has no anti-ferromagnetic material while the first magnetic layerhas an anti-ferromagnetic material therein, the first and secondmagnetic layers and have different materials. In certain embodiments,the second magnetic layer includes cobalt, nickel, iron or boron. Anexemplary formation method of the second magnetic layer includessputtering, PVD, ALD, e-beam or thermal evaporation, or the like.

In some embodiments where resistive random access memory (RRAM) cellsare to be formed on the wafer, the resistance switching layer 180 mayinclude a RRAM dielectric layer such as metal oxide composite, such ashafnium oxide (HfO_(x)), zirconium oxide (ZrO_(x)), aluminum oxide(AlO_(x)), nickel oxide (NiO_(x)), tantalum oxide (TaO_(x)), or titaniumoxide (TiO_(x)) as in its relative high resistance state and a metalsuch as titanium (Ti), hafnium (Hf), platinum (Pt), ruthenium (Ru),and/or aluminum (Al) as in its relative low resistance state.

Capping layers 190 and 200 are formed over the resistance switchinglayer 180. The capping layers 190 and 200 may include a thin metal-oxideor metal-nitride layer. The metal in the metal-oxide (or metal-nitride)capping layer includes beryllium (Be), magnesium (Mg), aluminium (Al),titanium (Ti), tungsten (W), germanium (Ge), platinum (Pt) and theiralloy. In some embodiments, the thickness of the capping layers 190 and200 is in a range from about 3 angstroms to about 20 angstroms. Thecapping layers 190 and 200 may be deposited by PVD, ALD, e-beam orthermal evaporation, or the like.

A top electrode layer 210 is formed over the capping layer 200. The topelectrode layer 210 includes a conductive material. In some embodiments,the top electrode layer 210 is similar to the bottom electrode layer 160in terms of composition. In some embodiments, the top electrode layer210 comprises titanium (Ti), tantalum (Ta), platinum (Pt), ruthenium(Ru), tungsten (W), aluminum (Al), copper (Cu), TiN, TaN, the like orcombinations thereof. An exemplary formation method of the top electrodelayer 210 includes sputtering, PVD, ALD, e-beam or thermal evaporation,or the like.

A hard mask layer 220 is formed over the top electrode layer 210 insequence. In some embodiments, the hard mask layer 220 is formed from adielectric material. For example, the hard mask layer 220 may be siliconcarbide (SiC), silicon oxynitride (SiON), silicon nitride (SiN), silicondioxide (SiO₂), ashing removable dielectric (ARD), the like, and/orcombinations thereof. In some embodiments, the hard mask layer 220 maybe formed from a conductive material. The hard mask layer 220 may beformed by acceptable deposition techniques, such as CVD, ALD, PVD, thelike, and/or combinations thereof.

Reference is made to FIG. 6. The hard mask layer 220, underlying topelectrode layer 210, and the underlying capping layer 200 are patterned.To be specific, a resist layer (not shown) is formed over the hard masklayer 220 and then patterned into a patterned resist mask using asuitable photolithography process, such that portions of the hard masklayer 220 are exposed by the patterned resist mask. In some embodiments,the patterned resist mask is a photoresist. In some embodiments, thepatterned resist mask is an ashing removable dielectric (ARD), which isa photoresist-like material generally having generally the properties ofa photoresist and amendable to etching and patterning like aphotoresist. An exemplary photolithography process may includephotoresist coating (e.g., spin-on coating), soft baking, mask aligning,exposure, post-exposure baking, developing the photoresist, rinsing,drying (e.g., hard baking), other suitable processes, or combinationsthereof.

An etching process is performed to remove portions of the hard masklayer 220, underlying top electrode layer 210, and the underlyingcapping layer 200 not protected by the patterned resist mask. The hardmask layer 220, underlying top electrode layer 210, and the underlyingcapping layer 200 may be etched using acceptable etching techniques,such as by using an anisotropic etching process. In some embodiments,the capping layer 190 may has a higher etch resistance to the etchingprocess than that of the capping layer 200. After the removal, cappinglayers 200′, top electrodes 210′, and hard mask covers 220′ remains asshown in FIG. 6. The patterned resist mask is removed using, forexample, an ash process, after the etching process.

Reference is then made to FIG. 7. An etching process is performed toremove exposed portions of the capping layer 190, underlying resistanceswitching layer 180, underlying buffer layer 170, and underlying bottomelectrode layer 160 not protected by the hard mask covers 220′ and thetop electrodes 210′. The capping layer 190, the resistance switchinglayer 180, the underlying buffer layer 170, and the underlying bottomelectrode layer 160 may be etched using acceptable etching techniques,such as by using an anisotropic etching process. After the etchingprocess, capping layers 190′, resistance switching elements 180′,underlying buffers 170′, and underlying bottom electrodes 160′ remain asshown in FIG. 7. The hard mask covers 220′ are removed after the etchingprocess.

In some embodiments, portions of the dielectric layer 140 not protectedby the hard mask covers 220′ and the top electrodes 210′ are alsoetched, and recesses R1 are formed in the remaining dielectric layer140′. The remaining dielectric layer 140′ includes portions 142 andportions 144. A height of the portions 142 is greater than that of theportion 144. For example, a top end of the portions 142 is higher thanthat of the portions 144. The portions 142 surround the BEVAs 150respectively. In some embodiments, a top end of the portions 142 isleveled up with the top surface of the BEVAs 150.

Reference is then made to FIG. 8. A first spacer layer 232 is blanketformed over the top electrodes 210′ and over sidewalls of the resistanceswitching elements 180′. Material of the first spacer layer 232 may beselected to protect the resistance switching elements 180′ withoutinfluencing the function of the resistance switching elements 180′. Forexample, the first spacer layer 232 may include suitable dielectricmaterials such as silicon nitride, silicon carbide, carbon-doped siliconnitride, carbon-doped silicon oxide, silicon oxynitride, other suitablematerials, and combinations thereof. In some embodiments, the firstspacer layer 232 may also be a composite layer including two or morelayers made of different materials, such as a silicon nitride/siliconcarbide stack. The first spacer layer 232 may be formed using CVD, PVD,ALD, the like, and/or combinations thereof.

FIG. 9 illustrates patterning of the first spacer layer 232. Thepatterning process removes horizontal portions of the first spacer layer232 while remaining vertical portions of the first spacer layer 232around the resistance switching elements 180′. The remaining portions ofthe first spacer layer 232 can be referred to as spacers 232′. In someembodiments, the spacers 232′ cover sidewalls of the resistanceswitching elements 180′ and leave the top electrodes 210′, portions ofthe capping layers 200′, and portions of the dielectric layer 140uncovered. In some embodiments, the patterning of the first spacer layer232 may include an etching process, such as an anisotropic etchingprocess using acceptable photolithography techniques. The patterningprocess may be dry etching, wet etching, or a combination thereof. Insome embodiments where the first spacer layer 232 is silicon nitride,the patterning of the silicon nitride layer includes a dry etching usingCH₂F₂, CF₄, CH_(x)F_(y), CHF₃, CH₄, N₂, O₂, Ar, He, as an etchant,although other applicable etchants may be used.

Reference is then made to FIG. 10. A second spacer layer 234 is blanketformed over the spacers 232′. The spacers 232′ may separate theresistance switching elements 180′ from the second spacer layer 234.Since the resistance switching elements 180′ is encapsulated by thespacers 232′, it is less likely that the second spacer layer 234influences the function of the resistance switching elements 180′, andtherefore the second spacer layer 234 may include a wider range ofmaterial than that of the first spacer layer 232. For example, thesecond spacer layer 234 includes suitable dielectric materials such assilicon nitride, silicon oxide, silicon carbide, carbon-doped siliconnitride, carbon-doped silicon oxide, silicon oxynitride, andcombinations thereof. The second spacer layer 234 may be made of thesame material as that of the spacers 232′. The second spacer layer 234may be formed using CVD, PVD, ALD, the like, and/or combinationsthereof. In some embodiments, a density of the second spacer layer 234is greater than a density of the spacer 232′. For example, in someembodiments the first spacer layer 232 and the second spacer layer 234are made of the same material, the first spacer layer 232 is formed at afirst temperature, the second spacer layer 234 is formed at a secondtemperature higher than the first temperature. In some embodiments, thesecond spacer layer 234 may also be a composite layer including two ormore layers made of different materials, such as a siliconnitride/silicon carbide stack.

FIG. 11 illustrates patterning of the second spacer layer 234. Thepatterning process removes horizontal portions of the second spacerlayer 234 while remaining portions of the second spacer layer 234 aroundthe resistance switching elements 180′ and the spacers 232′. Theremaining portions of the second spacer layer 234 can be referred to asspacers 234′. The spacers 234′ surrounds the spacers 232′. In someembodiments, the spacers 234′ cover sidewalls of the resistanceswitching elements 180′ and sidewalls of the capping layers 200′ andexpose the top electrodes 210′. In some embodiments, the spacers 234′around the resistance switching elements 180′ are connected. In someembodiments, the spacers 234′ are separated due to the patterningprocess.

In some embodiments, the patterning of the second spacer layer 234 mayinclude an etching process, such as an anisotropic etching usingacceptable photolithography techniques. The patterning process may bedry etching, wet etching, or a combination thereof. In some embodimentswhere the second spacer layer 234 is silicon nitride, the patterning ofthe silicon nitride layer includes a dry etching using CH₂F₂ as anetchant, although other applicable etchants may be used.

In some embodiments, the etching process to the second spacer layer 234may be stopped before reaching the dielectric layer 140, and therefore athin film of the spacers 234′ leaves over a top surface of thedielectric layer 140. For example, the spacers 234′ have a thin filmover the top surface of the dielectric layer 140 in the logic region LR.In some other embodiments, the dielectric layer 140 may have a higheretch resistance to the etching process than that of the second spacerlayer 234, such that the etching process to the second spacer layer 234may stop at the top surface of the dielectric layer 140, and leaves nothin film of the spacers 234′ over the top surface of the dielectriclayer 140.

Reference is then made to FIG. 12. Another ILD layer 240 is formed overthe substrate 110. In some embodiments, the ILD layer 240 may have thesame material as the ILD layer 112. In some other embodiments, the ILDlayer 240 may have a different material than the ILD layer 112. In someembodiments, the ILD layer 240 includes silicon oxide, fluorinatedsilica glass (FSG), carbon doped silicon oxide,tetra-ethyl-ortho-silicate (TEOS) oxide, phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), Black Diamond® (Applied Materials ofSanta Clara, Calif.), amorphous fluorinated carbon, low-k dielectricmaterial, the like or combinations thereof. An anti-reflection layerARL2, for example, a nitrogen-free anti-reflection layer (NFARL) isoptionally formed over the ILD layer 240. In some embodiments, thespacer 234′ may separate the spacer 232′ and the resistance switchingelements 180′ from the ILD layer 240.

Herein, a resist mask RM is formed over the ILD layer 240 and theanti-reflection layer ARL2. The resist mask RM is forming by patterninga resist layer (e.g., a photoresist layer) using a suitablephotolithography process. The resist mask RM covers the cell region CRand exposes the logic region LR.

Reference is made to FIG. 13. Portions of the anti-reflection layerARL2, the ILD layer 240, and the dielectric layer 140 in the logicregion LR are removed. The removal may be performed by an etchingprocess. In some embodiments where the ILD layer 240 is silicon oxide,the etchant used in the etching process can be dilute hydrofluoric acid(HF), HF vapor, CF₄, C₄F₈, CH_(x)F_(y), C_(x)F_(y), SF₆, or NF₃, Ar, N₂,O₂, He, gas. The resist mask RM acts as an etching mask during theetching process, and the elements in the cell region CR are protectedfrom being etched by the resist layer RM. The etch stop layer 120 has ahigher etch resistance to the etching process than that of the ILD layer240, such that the etching process in the logic region LR stops at theetch stop layer 120. After the etching process, the anti-reflectionlayer ARL2, the ILD layer 240, and the dielectric layer 140 are not inthe logic region LR. Herein, the etch stop layer 120 has a first portion122 in the cell region CR and a second portion 124 in the logic regionLR, and after the removal, the second portion 124 of the etch stop layer120 is exposed.

Reference is made to FIG. 14. Another ILD layer 250 is formed over thesubstrate 110. Since the ILD layers 240 and 250 are formed at differentoperations, there is a clear interface 51 between the ILD layers 240 and250. Also, since the ILD layer 250 and the dielectric layer 140 areformed at different operations, there is a clear interface S2 betweenthe ILD layer 250 and the dielectric layer 140.

In some embodiments, the ILD layer 250 may have the same material as theILD layer 240 or the dielectric layer 140. In some other embodiments,the ILD layer 250 may have a different material than the ILD layer 240or the dielectric layer 140. In some embodiments, the ILD layer 250includes silicon oxide, fluorinated silica glass (FSG), carbon dopedsilicon oxide, tetra-ethyl-ortho-silicate (TEOS) oxide, phosphosilicateglass (PSG), borophosphosilicate glass (BPSG), Black Diamond® (AppliedMaterials of Santa Clara, Calif.), amorphous fluorinated carbon, low-kdielectric material, the like or combinations thereof. Ananti-reflection layer ARL3, for example, a nitrogen-free anti-reflectionlayer (NFARL) is optionally formed over the ILD layer 250.

Reference is made to FIG. 15. A metallization pattern 270 is then formedin the ILD layer 250. Formation of the metallization pattern 270 may beformed by etching openings O2 in the ILD layer 250, etching openings O3in the second portion 124 of the etch stop layer 120, and then fillingone or more metals (e.g., copper) in the openings O2 and O3 to form themetallization pattern 270. In some embodiments where the ILD layer 250is silicon oxide, the etchant used in etching the openings O2 can bedilute hydrofluoric acid (HF), HF vapor, CF₄, C₄F₈, CH_(x)F_(y),C_(x)F_(y), SF₆, or NF₃, Ar, N₂, O₂, Ne, gas. In some embodiments, theetch stop layer 120 may has a higher etch resistance to the etching theopenings O₂ than that of the ILD layer 250. The etching the openings O2may stop at the etch stop layer 120 and not damage the underlying ILDlayer 112. After the openings O2 and O3 are filled with metals, aplanarization is performed to remove an excess portion of the metalsoutside the openings O2, and therefore the metallization pattern 270 isformed. In some embodiments, portions of the spacers 234′ and the topelectrodes 210′ are also removed by the planarization, and the remainingspacers 234′ covers sidewalls of the remaining top electrodes 210′ andleaves top surfaces of the remaining top electrodes 210′ uncovered.Through the configuration, the metallization pattern 270 can reach andelectrically connect the metallization pattern 114.

Reference is made to FIG. 16. A etch stop layer 280 and an ILD layer 290are formed over the resulting structure of FIG. 15. The etch stop layer280 may have the same material as that of the etch stop layer 120. Theetch stop layer 280 may be formed of dielectric material different fromthe underlying ILD layers 240 and 250. For example, the ILD layers 240and 250 may be a silicon oxide layer, and the etch stop layer 280 may bea silicon nitride layer or a SiC layer.

In some embodiments, the ILD layer 290 may have the same material as theILD layers 240 and 250. In some other embodiments, the ILD layer 290 mayhave a different material than the ILD layers 240 and 250. In someembodiments, the ILD layer 290 includes silicon oxide, fluorinatedsilica glass (FSG), carbon doped silicon oxide,tetra-ethyl-ortho-silicate (TEOS) oxide, phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), Black Diamond® (Applied Materials ofSanta Clara, Calif.), amorphous fluorinated carbon, low-k dielectricmaterial, the like or combinations thereof.

Reference is made to FIG. 17. Holes or openings O4 are etched in the ILDlayer 290 by a first etching process, and openings O5 are etched in theetch stop layer 280 by a second etching process. The holes or openingsO4 and O5 expose the top surface of the top electrodes 210′ in the cellregion CR and the metallization pattern 270 in the logic region LR. Theetch stop layer 280 has a higher etch resistance to the first etchingprocess than that of the ILD layer 290, such that the first etchingprocess stops at the etch stop layer 280. In some embodiments where theILD layer 290 is silicon oxide, the etchant used in the first etchingprocess can be dilute hydrofluoric acid (HF), HF vapor, CF₄, C₄F₈,CH_(x)F_(y), C_(x)F_(y), SF₆, or NF₃, Ar, N₂, O₂, He, gas.

In some embodiments, the top electrodes 210′ have a higher etchresistance to the second etching process than that of the etch stoplayer 280, such that the second etching process stops at the topelectrodes 210′. In some embodiments, the spacers 234′ has a higher etchresistance to the second etching process than that of the etch stoplayer 280 and that of the spacers 232′, such that when the holes oropenings O4 and O5 are large enough to expose the spacers 234′, thesecond etching process may be stopped by the spacers 234′. For example,in the second etching process, an etch rate of the spacers 234′ isslower than that of at least one of the etch stop layer 280 and thespacers 232′. Through the configuration of the spacers 234′, theresistance switching elements 180′ and the spacers 232′ are protectedduring the second etching process, and the process window of the etchingprocess can be enlarged.

Reference is made to FIG. 18. One or more metals (e.g., copper) in theholes or openings O4 and O5 to form the metallization pattern 300. Afterthe holes or openings O4 and O5 are filled with metals, a planarizationis performed to remove an excess portion of the metals outside the holesor openings O4, and therefore the metallization pattern 300 is formed.Through the configuration, the metallization pattern 300 can reach andelectrically connect the metallization pattern 270 and the topelectrodes 210′.

FIG. 19 illustrates an integrated circuit including MRAM devices andlogic devices. The integrated circuit includes a logic region 900 and aMRAM region 910. Logic region 900 may include circuitry, such as theexemplary transistor 902, for processing information received from MRAMdevices 920 in the MRAM region 910 and for controlling reading andwriting functions of MRAM devices 920. In some embodiments, the MRAMdevice 920 includes an MTJ stack 922, a top electrode 923 over the MTJstack 922, and a bottom electrode 924 under the MTJ stack 922, andspacers 925 and 926 surrounds the top electrode 923, the MTJ stack 922,and the bottom electrode 924.

As depicted, the integrated circuit is fabricated using sixmetallization layers, labeled as M1 through M6, with six layers ofmetallization vias or interconnects, labeled as V1 through V6. Otherembodiments may contain more or fewer metallization layers and acorresponding more or fewer number of vias. Logic region 900 includes afull metallization stack, including a portion of each of metallizationlayers M1-M6 connected by interconnects V2-V6, with the interconnect V1connecting the stack to a source/drain contact of logic transistor 902.The MRAM region 910 includes a full metallization stack connecting MRAMdevices 920 to transistors 912 in the MRAM region 910, and a partialmetallization stack connecting a source line to transistors 912 in theMRAM region 910. MRAM devices 920 are depicted as being fabricated inbetween the top of the metallization layer M4 and the bottom of themetallization layer M6. The metallization layer M4 is connected with thebottom electrode 924 through a bottom via in an etch stop layer 940 anda dielectric layer 950, and the metallization layer M6 is connected withthe top electrode 923 through the interconnect V6 in an etch stop layer930. Also included in integrated circuit is a plurality of ILD layers.Seven ILD layers, identified as ILD0 through ILD6 are depicted in FIG.14 as spanning the logic region 900 and the MRAM region 910. The ILDlayers may provide electrical insulation as well as structural supportfor the various features of the integrated circuit during manyfabrication process steps.

Based on the above discussions, it can be seen that the presentdisclosure offers advantages. It is understood, however, that otherembodiments may offer additional advantages, and not all advantages arenecessarily disclosed herein, and that no particular advantage isrequired for all embodiments. One advantage is that the resistanceswitching element is protected by two spacers from moisture andoxidation. Another advantage is that one of the spacers may have ahigher etch resistance to an etching process for metallization pattern,such that the punching trough issue is prevented. Still anotheradvantage is that the process window for the etching process formetallization pattern can be enlarged.

According to some embodiments of the present disclosure, a deviceincludes a conductive feature, a dielectric layer, a bottom electrodevia, and a liner layer. The dielectric layer is over the conductivefeature. The bottom electrode via is in the dielectric layer and overthe conductive feature. A topmost surface of the bottom electrode via issubstantially flat. A liner layer cups an underside of the bottomelectrode via. The liner layer has a topmost end substantially levelwith the topmost surface of the bottom electrode via.

According to some embodiments of the present disclosure, a deviceincludes a conductive feature, a dielectric layer, a bottom electrode,and a metal-containing layer. The bottom electrode is in the dielectriclayer and over the conductive feature. A topmost surface of the bottomelectrode is substantially flat. The metal-containing layer surroundsthe bottom electrode and between the bottom electrode and the dielectriclayer. The metal-containing layer has a topmost surface surrounding andsubstantially aligned horizontally with the topmost surface of thebottom electrode.

According to some embodiments of the present disclosure, a deviceincludes a conductive feature, a dielectric layer, a bottom electrodevia, a diffusion barrier layer, a bottom electrode layer, a resistanceswitching element, and a top electrode. The dielectric layer is over theconductive feature. The bottom electrode via is in the dielectric layerand over the conductive feature. The diffusion barrier layer is betweenthe bottom electrode via and the conductive feature. The bottomelectrode layer is over the bottom electrode via and the diffusionbarrier layer, in which a bottom surface of the bottom electrode layeris substantially flat. The resistance switching element is over thebottom electrode layer. The top electrode is over the resistanceswitching element.

According to some embodiments of the present disclosure, a deviceincludes a dielectric layer, a bottom electrode structure, a metal viastructure, and a metal layer. The bottom electrode structure is embeddedin the dielectric layer, the bottom electrode structure includingtantalum nitride. The metal via structure provides a conductive pathwayto the bottom electrode structure and an underlying interconnectstructure, the metal via structure including titanium, titanium nitride,tantalum, tantalum nitride, tungsten, or combinations thereof. The metallayer is intermediate the bottom electrode structure and the metal viastructure, the metal layer including titanium nitride, tantalum nitrideor combinations thereof.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device, comprising: a conductive feature; adielectric layer over the conductive feature; a bottom electrode via inthe dielectric layer and over the conductive feature, wherein a topmostsurface of the bottom electrode via is substantially flat; and a linerlayer cupping an underside of the bottom electrode via, wherein theliner layer has a topmost end substantially level with the topmostsurface of the bottom electrode via.
 2. The device of claim 1, furthercomprising: a resistance switching element over the topmost surface ofthe bottom electrode via and the topmost end of the liner layer.
 3. Thedevice of claim 1, wherein the liner layer is in contact with theconductive feature.
 4. The device of claim 1, wherein the topmost end ofthe liner layer is substantially level with a top surface of thedielectric layer.
 5. The device of claim 1, wherein the liner layerspaces the bottom electrode via from the dielectric layer.
 6. The deviceof claim 1, further comprising: a bottom electrode layer extendingacross the bottom electrode via and the liner layer.
 7. A device,comprising: a conductive feature; a dielectric layer over the conductivefeature; a bottom electrode via in the dielectric layer and over theconductive feature; a diffusion barrier layer between the bottomelectrode via and the conductive feature; a bottom electrode layer overthe bottom electrode via and the diffusion barrier layer, wherein abottom surface of the bottom electrode layer is substantially flat; anda resistance switching element over the bottom electrode layer; and atop electrode over the resistance switching element.
 8. The device ofclaim 7, wherein the bottom surface of the bottom electrode layer is incontact with the bottom electrode via and the diffusion barrier layer.9. The device of claim 7, wherein the bottom surface of the bottomelectrode layer covers the bottom electrode via, the metal-containinglayer, and a portion of the dielectric layer.
 10. The device of claim 7,wherein a top surface of the dielectric layer has a portion free ofcoverage by the bottom electrode layer, and the portion of the topsurface of the dielectric layer is lower than the bottom surface of thebottom electrode layer by a step height.
 11. The device of claim 7,wherein a top surface of the dielectric layer has a portion in contactwith the bottom surface of the bottom electrode layer.
 12. The device ofclaim 7, wherein a sidewall of the resistance switching element issubstantially aligned with a sidewall of the bottom electrode layer. 13.A device, comprising: a dielectric layer; a bottom electrode structureembedded in the dielectric layer, the bottom electrode structurecomprising tantalum nitride; a metal via structure providing aconductive pathway to the bottom electrode structure and an underlyinginterconnect structure, the metal via structure comprising titanium,titanium nitride, tantalum, tantalum nitride, tungsten, or combinationsthereof; and a metal layer intermediate the bottom electrode structureand the metal via structure, the metal layer comprising titaniumnitride, tantalum nitride or combinations thereof.
 14. The device ofclaim 13, wherein a top surface of the bottom electrode structure issubstantially flat, and a top surface of the dielectric layer has aportion substantially level with the top surface of the bottom electrodestructure.
 15. The device of claim 13, wherein the metal layer cups anunderside of the bottom electrode structure.
 16. The device of claim 13,wherein the metal layer has a top end substantially level with a topsurface of the bottom electrode structure.
 17. The device of claim 13,wherein a top surface of the dielectric layer is free from coverage bythe metal layer.
 18. The device of claim 13, further comprising: aresistance switching element over the bottom electrode structure. 19.The device of claim 18, wherein the resistance switching element has abottom width greater than a top width of the bottom electrode structure.20. The device of claim 13, wherein the metal layer is on sidewalls ofthe bottom electrode structure.